Numerous methods and apparatus are known in the art which involve the use of a torch for working materials. The use of flame cutting has the disadvantage that it is only applicable to easy-to-oxidize materials such as structural steel. Another type of torch cutting, known as flux-injection cutting is undesirable from the stand point that it creates flux material pollution in the form of fine articles of aluminum, iron, sand, etc. Plasma cutting, yet another type of cutting, is limited in terms of its effectiveness for cutting non-metallic materials (non-conductors of electrical current), and limited effectiveness in cutting materials having a thickness more than 40 mm. Moreover, high temperatures in the working area (more than 10,000.degree. C.) result in intensive sublimation of the material being worked and its oxides which makes this method ecologically detrimental.
Also known in the art is a method of breaking down rocks with the aid of high temperature supersonic jet as disclosed in USSR Author's certificate #924370, Int. Cl. E 21 C 3716, 1982. However, this method is unsuited for torch working different materials since it has no provisions for changing jet parameter values.
A method and apparatus are also known in the art for flame cutting steel which are disclosed in USSR Author's Certificate No. 155146, Int. Cl. F23D 14/46, 1963. This method comprises providing a fuel and an oxidizer, mixing the fuel with the oxidizer into a propellant, burning the propellant mixture under high pressure, forming a gaseous jet of products of combustion, and acting upon the material with the gaseous jet. The apparatus used to practice this method contains a cutting head and a grip accommodating tubes for oxygen and fuel supply. The cutting head comprises a mixer including a housing, a perforated spacer, and a torch tip. Passages are formed in the housing to deliver propellant components to two rows of through openings concentrically located on the spacer-for oxygen and fuel delivery, and to the central opening for delivery of cutting oxygen. An inner space of the torch tip includes a combustion chamber where propellant components are mixed, burnt and evaporated.
The disadvantage of the flame cutting method and apparatus mentioned above is low effectiveness in cutting a number of materials. Specifically, it was difficult to work reinforced concrete and brickwork; aluminum alloys forming refractory oxides; oxidation-resistant products as stainless steel; pig iron containing high amounts of silicon and forming slags which are difficult to carry away from the cutting area.
The disadvantage mentioned above results from low efficiency in burning the propellant components (the fuel and the oxidizer) which in turn results from arranging the openings for delivery of fuel and oxidizer in the same plane of the section of the apparatus. As a matter of fact, the effectiveness of mixing the propellant components immediately depends on the precision in making and mutual arranging of the sloping openings for the fuel and oxidizer. It is only in an ideal case where the openings are manufactured absolutely precisely, that the fuel and oxidizer flowing out of them would collide at a predetermined point. In practice, however, variations always exist in the angles of slope of the openings, in their spacing relative to the apparatus axis of symmetry, in their angular arrangement at the spacer plane, in the geometry of front and rear edges of the openings, as well as some degree of roughness and soiling of their inner passages, inhomogeneity of speed field in ring-shaped bores, etc. Under these circumstances, mixing of the propellant components occurs under imperfect conditions, and completeness of combustion of the propellant within restricted space of the tip is not high.
There is also a loss of the propellant components upon their firing, and pulling a torch into the tip (the combustion chamber). Time is to be spent for forming a supersonic jet outflowing from the tip which needs mixing propellant components, firing the propellant mixture, and regulating flame parameters in order to ensure propagating of the flame edge back into the tip. All these operations necessitate definite skills and qualification of a cutter. Improper performing them may result in either flame-out and flame failure or flame edge penetrating into the mixer and popping that causes the flame to have to be extinguished. Such loss may have a significant bearing on effectiveness of the apparatus, especially where the process of cutting a structure (such as an aircraft) may necessitate moving therealong, with the torch burner being turned on and off.
It is therefore an object of the invention to provide new method and apparatus with enhanced effectiveness in torch working materials of different properties and width which results from reduction of propellant (fuel and oxidizer) consumption at the starting-up moment owing to decrease of starting-up time.
The method of torch working materials according to the present invention comprises the steps of providing a fuel and an oxidizer, mixing them with each other into a propellant, burning the propellant mixture under high pressure, forming a supersonic nonoverwidened gaseous jet out of products of combustion and acting upon the material with the gaseous jet. A speed ratio of the gaseous jet speed (v), acting upon the material, to the speed of sound (a) in the jet is to be chosen in the range of 1.1 to 4.8; a temperature ratio of the jet temperature (T.sub.c) to the melting point (T.sub.m) of the material is to be chosen in the range of 1.2 to 4.5. Additionally, the factor (.alpha.) of the oxidizer excess relative to a stoichiometric ratio of propellant components is to be chosen in the range of EQU 3.4.ltoreq..alpha..ltoreq.4.9
for easy-to-oxidize materials, and in the range of EQU 0.44.ltoreq..alpha.&lt;3.4
for non-oxidizable materials and materials forming refractory oxides. The above mentioned factor .alpha. is a fraction with a real mass ratio of the propellant components in the numerator and the stoichiometric ratio of the propellant components, providing complete combustion thereof, in the denominator.
One important facet of the method lies in using a supersonic, concentrated, high-temperature (up to 4000.degree. C.) jet. In this connection, three factors have an effect on the material. Specifically, they are: a temperature action resulting in melting the material down; a chemical attack by the chemically active jet for oxidizing the material; and an erosional action consisting in blowing the melted material along with its oxides out of the working area by the jet head.
It is the cooperative action of the basic elements of the jet, namely,
forming the jet by burning fuel (specifically kerosene-gasoline or ethylmethyl alcohol) and oxidizer (specifically oxygen) at elevated pressure as compared with the ambient pressure surrounding the material; PA1 nonoverwideness of the jet; PA1 the jet speed and temperature ranges; and PA1 ranges of the oxidizer excess factor (chemical composition of the jet), PA1 at falling outside the upper limit of the v/a range, the gas flow approaches the hypersonic one. The technical implementation of apparatus with such kind of gas flow is complex and unsuitable economically. PA1 At falling outside the lower limit of the v/a ratio, the supersonic jet flow becomes unstable which results from flow nonideality and technological imperfectness of making a gas dynamic path. The unstableness of supersonic flow considerably decreases the effectiveness of the process. PA1 Using a supersonic jet having the temperature ratio T.sub.c /T.sub.m less than 1.2 decreases the effectiveness of torch working, and it may even fall down to zero because of heat loss due to heat conduction of the material and natural convection. Falling outside the upper limit of the chosen T.sub.c /T.sub.m range (beyond 4.5) may cause volatilization of the material being worked, and, hence, discharge into the open air of fumes of such unhealthy steel alloy addings as chromium, molibdenum, berillium, nickel, etc., which may result in ecological impurity of the process, and the necessity of taking certain arrangements to protect the personnel and environment. Eventually, that will lower effectiveness of the process. PA1 Maintaining chemical composition of the jet variable for different easy-to-oxidize and oxidation-resistant materials within the above limits enables to effectively cut and work the relevant materials and structures therefrom, with the least consumption of the propellant components possible.
that contributes to the above-mentioned factors and makes accomplishment of the object of the invention possible.
As used herein, the term "nonoverwideness" is intend to mean that the jet as delivered to the working area possesses a static pressure that is equal to or greater than the ambient pressure so that it is sufficiently concentrated to be highly penetrating and hence effective. It is understood that the various feature dimensions and ratios, and specific geometries are to be selected so as to produce a "nonoverwidened" jet having this characteristics.
At the same time, it has been established analytically and experimentally that:
According to the present invention, an apparatus (which is hereinafter also referred to as a burner) comprises a cutting head containing a torch tip and a mixer defining in cooperation an inner space of the cutting head, and a grip, including pipelines with flow control elements, for delivery of an oxidizer and a fuel from their sources. The mixer has openings connected, on one side, with the pipelines, and with the inner space of the cutting head, on another side. The mixer includes a housing having an inner space communicating with an inner space of the torch tip, the openings in the housing of the mixer being formed on different levels with respect to flow. The opening for fuel delivery is formed in a side part of the housing of the mixer and located downstream in respect to the opening for delivery of the main oxidizer. The ratio of the hydraulic diameter d.sub.h-fo at the outlet from the opening for fuel delivery into the inner space of the mixer to the hydraulic diameter d.sub.h-mis of a flow section of the inner space of the mixer at the point of the introduction the fuel into the inner space of the mixer is to be assigned within the range of 0.03 to 0.5.
By hydraulic diameter d.sub.h, the term well-known to those skilled in the art of fluid mechanics, the definition d.sub.h =4S/P is meant, where S is flow section area of a passage, and P is its wetted circumference. In particular case of a circular opening, its diameter is obviously the hydraulic diameter of the flow section of the circular opening.
The mixer inner space is provided with a central body axially installed in that space, and hermetically secured in the top opening of the housing, with one end of the central body outwardly projecting from the housing. The central body acts as a unit for controlling thermodynamic parameters of the propellant mixture flow. The central body is activated by a drive cooperating with the part of the central body outwardly projecting beyond the mixer housing.
Effectiveness enhancement of the invention as compared to the prior art results from forming an area of bottom rarefaction beyond the face of the central body located in the mixer inner space. As it is well known to those skilled in the art of gas dynamics, gas flow structure in such area is vortical in its effect. High degree of turbulence of the vortical structure contributes to high homogeneity of the fuel and oxidizer propellant mixture prepared previously upstream. Specifically, it has been experimentally found that the jet concentration, in the case of gaseous oxygen and small fuel drops (less than 40 .mu.m) previously mixed in the mixer inner space, is getting practically equalized due to high extent of turbulence.
The above range of d.sub.h-fo to d.sub.h-mis ratio has been ascertained experimentally. Upon falling outside the recommended range, propellant mixture tends to segregate into layers which reduces effectiveness of the apparatus and increases a probability of its failure as a result of the central body or housing outburning.
Falling outside the lower limit of the range corresponds to an increased fuel momentum relative to an oxidizer momentum that results in fuel concentrating around the central body, distorting propellant mixture forming process, and eventually outburning of the central body face part.
Falling outside the upper limit of the diameter ratio corresponds to a reduced fuel momentum as to oxidizer momentum. In consequence, the fuel concentrates by the inner surface of the mixer, scheme of propellant mixture forming gets distorted again, and outburning of the mixer housing becomes possible.
The central body of the apparatus at issue provides controlling thermodynamic parameters of the fuel and oxidizer propellant mixture, along with participation in the very process of formation the propellant mixture. Those skilled in the art of fluid mechanics are cognizant of speed, pressure and temperature of a flow being its main parameters. These are the very parameters defining effectiveness of the process of torch working materials. To control these parameters with the help of the central body is proposed by means of supplying additional energy through the central body to the flow, either changing its speed field, or introducing an additional mass of a gas into the flow, or both.
With these and other objects and advantages in view, the present invention will be clearly understood from the ensuing detailed description in connection with the accompanying drawings.